MP3309C LED Driver Efficiency and Reference Schematic

DC-DC Power Converters
1

Hi,

  1. Is there any efficiency data for the MP3309CGQG? I would like to use a efficiency value to calculate the required inductance and determine power dissipation of the chip.

  2. In the reference schematics in the MP3309CGQG datasheet there is a 150ohm series resistor on the booststrap pin (pin 9) that is not mentioned anywhere else in the datasheet. Is that 150ohm resistor necessary?

2

Hi Neville,

You can refer to the efficiency graph in the datasheet.
image

Typically, the bootstrap resistor slows down the switch turn on to reduce the switch node ringing.

Best Regards,
Yu

4

Thank you for the response. The efficiency curve assumes 20mA but I plan to drive this at much higher current.

What is the maximum continuous LED current that this driver (MP3309C) supports?

I am trying to design this driver to power 2 LEDs with 6.2V output voltage and 0.5A continuous current. Will this driver be able to handle this? The datasheet states a maximum cycle to cycle current but that doesn’t sound like it applies to this question.

5

Hi Neville,

This may depend on your duty cycle which depends on factors like your input.
The 1.5A refers to the max switch current and because this is a boost, you should be able to calculate if you are going to reach this limit.

If this one does not work out, we do have higher current boost LED drivers.
Backlight Voltage Drivers (WLED) | Display Backlighting Power | MPS | Monolithic Power Systems

Best Regards,
Yu

6

Hi Yu,

Thanks. The input voltage is between 4.4-5.5V so I calculated 133mA max continuous current assuming 80% efficiency.

In the application, the LEDs will only be turned on for a short duration of about ~100ms at a time. Is there a way to figure out what the shortest time duration we can flash the LEDs at 0.5A if its possible?

Lastly, I took a look at those other drivers from your link. If the multi-channel driver outputs can be “ganged” or connected together to support my 0.5A output requirement, then I think MPS may have a solution for this. If you have any recommendations our requirements are below:

  1. Two neutral white LEDs in series with max 7.5V forward voltage and 500mA max forward current.
  2. The LED driver must provide constant current, but it can be set via I2C bus from 0mA to 500mA in 32 or higher incremental steps.
  3. Input voltage of 4.4V-5.5V.
7

Hi Neville,

For single channel, we do have parts such as MP3370 that can support higher peak switch current.

Best Regards,
Yu